As a delayed action preparation providing for a lag time in the release of an active ingredient, the preparation comprising a drug, a swelling agent and a water-insoluble coating material and wherein said swelling agent is contained in a sufficient amount to explode an outer membrane of the water-insoluble coating material at a definite time after administration is disclosed in Japanese Patent Application Kokai S-62-30709.
Meanwhile, a microencapsulated dosage form comprising a core containing a drug and a drug reservoir therefor, such as gelatin, and a biodegradable high molecular weight substance as a coating material is known from Japanese Patent Publication S-60-100516.
The preparation described in Japanese Patent Publication Kokai S-62-30709 referred to above, the outer membrane of which is made of a water-insoluble coating material such as ethylcellulose has the disadvantage that the outer membrane which is not decomposed or solubilized in the body fluid remains in the body even after releasing the drug. Therefore, although the residual outer membrane substance is excreted from the body rather easily after oral administration, it is hardly excreted when the preparation is administered intramuscularly, subcutaneously or otherwise.
The preparation disclosed in Japanese Patent Publication Kokai S-60-100516 is disadvantageous in that because the volume of the drug reservoir is small, the outer membrane is not exploded and although the drug is released gradually with progressive decomposition of the outer membrane, the pattern and rate of drug release cannot be-freely controlled and, the release after a designed lag time cannot be expected.